Pretty simple problem that apparently was experienced by a lot of people in MOSS, but extensive research has produced exactly zero answers.
Environment: 2010 SP1 August CU, single-server farm with separate SQL server, Exchange 2010 on another server, ~150 users
I have a large asset library that is very active. Dozens of users make changes and upload new files daily. One particular manager has a single alert set on the library to give him a daily summary at 8AM of all changes made by anyone. The full summary contains 30-100 items. But for this one alert for this one user (it's the only alert he has) he receives all the changes split across multiple emails. Usually they have about 2 items a piece and some of them are often duplicated in other emails.
I've tried deleting and recreating the alert, but the same symptoms occur every time. It is consistent, at least, and I've set up some other alerts to see if it happens to multiple users or just him. So far one of those alerts has fired and worked normally, but it only contained two changes anyways. Have more set up later in the day to catch more activity, will update this post when I have results.
Update: The test alerts are all in and working perfectly (and include dozens of changes in a single email, not broken up). These alerts were created for and by a normal user account that I use for testing, but are otherwise identical to the alert the user in question is having problems with. My coworker suggested it may be a problem with the user account itself and recommended deleting and recreating it entirely, but I would rather avoid that if possible because it would break any metadata or other setting associated with the account. Could that really be the solution though?
Further Updates: I hate to say it but I'm experiencing the same behavior described by many other people back in v3, despite me being on up-to-date v4. The alert for the user in question magically fixed itself, but the same kind of alert for another user just broke and sent them 500+ emails for what was supposed to be a daily summary. Meanwhile my test accounts have experienced no problems whatsoever with the exact same alerts.